Photochemical behaviour of Fisetin and Fisetin-Copper(II)

VANESA A. MUÑOZ; FRIDA C. D. DIMARCO; SADRA MISKOSKI; GABRIELA V. FERRARI; NORMAN A. GARCÍA; M. PAULINA MONTAÑA

Villa Carlos Paz, Córdoba, Argentina

Congreso; XIII LATIN-AMERICAN MEETING ON PHOTOCHEMISTRY AND PHOTOBIOLOGY; 2017

Asociación de fotoquímica y fotobiología

Results and discusions: The Riboflavin (Rf)-sensitized photoirradiation of Fis and Fis-Cu(II) at H2O/EtOH 70:30 v/v medium produced spectral changes that can be attributed to transformations in both substrates. The oxygen uptake in presence and absence of specific quencher of reactive oxygen species (ROS) made evident the interaction between Fis and H2O2, showed by the decrease of the O2 consumption rate in presence of catalase, whereas in the case of Fis-Cu(II) complex the experimental results allow to confirm the participation of the O2?- species in the oxidative process, but no significant evidence of singlet molecular oxygen (O2(1Δg)) interaction was observed. Nevertheless, on the basis of our previous investigations where this ROS usually plays a rol in the photooxidative mechanism of flavonoids, the rate constant for the overall interaction with O2(1Δg), kt, was determined through a Stern-Volmer treatment (see values in the table). The phosphorescence quenching experiments demonstrated the existence of a O2(1Δg)-Fis and Fis-Cu(II) interaction. The reactive O2(1Δg) quenching constants (kr) were determinated for both systems and are showed in the table.Systemkt x 10-7 M-1s-1kr x 10-7 M-1s-1kr/ktFis14.40.260.02Fis-Cu(II)7.252.660.36The kr/kt ratio is an useful parameter of the substrate oxidability since indicates the fraction of overall quenching of O2(1Δg) that effectively leads to a chemical transformation. It can be seen that the interaction of Fis-O2(1Δg) is exclusively physical. On the other hand, the metallic complexation of the flavonol increases the reactive fraction, reaching 36 % of the overall interaction. The anaerobic photodegradation of Rf under visible light irradiation predominantly proceeds through the triplet state [2], and the rate of the process can be estimated by absorption spectroscopy. Comparative irradiations of N2-saturated ethanolic solutions of Rf under identical experimental conditions, in the absence and in the presence of either Fis or its metallic complex were carried out. Hence, data were evaluated through a simple Stern-Volmer treatment being the apparent rate constant values for the process of quenching of 3Rf∗ close to 1,4x1010 M-1s-1. This step could contribute to decrease the stationary concentration of O2(1Δg) and, therefore, to present a protective effect against this species.